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In the past few years, engine power ratings have steadily increased. To meet the demand of engine and vehicle manufacturers for a transmission to match these larger engines, Detroit Diesel Allison developed the CLBT9680 transmission. This transmission has been designed and developed to operate in rear-dump trucks up to 127 tonne (140-ton) capacity, and in bottom- or side-dump trucks up to 154 tonne (170-ton) capacity. In these applications the CLBT9680 has a power rating up to 1007 kW (1350 ghp). The transmission can also be approved with engines rated up to 1093 kW (1465 ghp) in special purpose installations such as oil field service equipment. In this paper the transmission design and test development programs are presented. In addition, the extensive development programs are discussed relative to performance and reliability goals for the transmission.

Since the first passenger coaches were built in the early 1900's, coach manufacturers have sought better and better engine-transmission combinations and arrangements in order to improve performance, operation, and passenger convenience. As the coach industry entered the 1970's, it became increasingly obvious that a need existed for a new transmission to replace those of the old V-family that provided the bulk of the market for the past 40 years. Recognizing the need, Detroit Diesel Allison developed two new transmissions, the HT 740 and the V730, for the coming generation of coach applications. These two units permit a number of engine-transmission-axle arrangements and are adaptable to diesel and gas turbine engines. It is anticipated that these units will find wide usage in new coaches currently under development.

Because of the increasing complexity of commercial trucking operation and management, the truck automatic transmission is being found to be an asset in terms of overall vehicle economics-in addition to its long recognized features of ease of operation and safety. A number of salient vehicle cost factors upon which the truck automatic transmission has an impact are discussed-along with the transmission design principles which lead to that impact. Acceptance of this premise by the trucking industry is shown by market segment. In addition to discussing the contribution of the truck automatic transmission toward improving the overall economics position of today's commercial vehicles, this paper gives indication of forthcoming refinements in transmission design which will further reduce fuel consumption costs.

The continuing improvement and development of off-highway working vehicles has demanded corresponding continuing advancements in transmission technology. As a result Detroit Diesel Allison will introduce, in 1973, the Allison CLBT 750 fully automatic transmission for service in the off-highway market of 20 to 35-ton trucks and 15 to 20-yard scrapers. The CLBT 750 transmission was designed as a five-speed unit with automatic shift modes for second through fifth ranges. Design activity on the transmission included development of a hydraulic controls system which would provide optimum shifting for all conditions of engine and vehicle speeds and loads while ensuring that those shifts, both up and down, are smooth, positive, and safe. The design activity also included development of a minimum size, high capacity, highly responsive retarder to ensure safe descent of steep grades.

The Type C-3 transmission fluid specification has been completed which defines tighter requirements for fluids used in heavy-duty off-highway automatic or power shift transmissions. A laboratory test program was conducted to develop and prove-out the uprated requirements. The C-3 specification now provides for control of the fluid's effect on clutch friction retention and durability. A redefined oxidation stability test has been included which calls for the use of test hardware that is more readily available. Seal-swell requirements were expanded to include the latest materials used in transmission seals. The cooperative efforts of the petroleum and additive industries, along with Detroit Diesel Allison, are now providing an improved fluid for use in the latest off-highway heavy-duty transmissions.

Detroit Diesel Allison introduced it's first electronic controlled transmission, the DP 8000 series transmission, in 1971 with the discrete lope shift pattern generator (SPG). In 1983, a new state-of-the-art digital electronic control option called ATEC (Allison Transmission Electronic Control) was offered on the V 730 series transit coach transmission. ATEC was introduced to the HT 700 series transmission including the CLBT 755 series off-highway transmissions in 1984. In January 1986, the ATEC system replaced the current SPG electronics across the board on 5, 6, 8, and 9000 series off-highway transmissions. ATEC provides greater capability and increased reliability at a reduced cost over the SPG electronics. The ATEC system is currently in a field test program that will continue through the first year of production to monitor its reliability improvement over the SPG system. Controlled testing to SAE standards have quantified fuel economy and productivity gains with ATEC.